By Rudiger Safranski, Martin Heidegger: Between Good and Evil. (Harvard University Press, 474 pp.)

"Moths fly into the light." So Heidegger's most prominent student, Hans-Georg Gadamer, characterized Heidegger's effect on his students at the University of Marburg in the 1920s. Although Heidegger expressed doubts about whether he would ever be capable of any original philosophical insights, he rightly described himself as a kind of museum attendant, pulling back the curtain on the philosophy of the past.

Given Heidegger's view of truth as aletheia--"unconcealment" which takes place in a moment of insight--it was appropriate that he was so gifted at illuminating such thinkers as Aristotle and Kant by making them speak to our time. What Heidegger teaches us (and what makes him perhaps the greatest philosopher of our century) is the art of rethinking old philosophical questions in dramatically new ways.

If philosophy is the art of asking questions, then Heidegger was truly a master. But, as Rüdiger Safranski makes clear throughout his carefully researched, philosophically informed and remarkably lucid account of Heidegger's development, the master of questions was considerably less a master of answers. Indeed, a former Marburg colleague who later vied with Heidegger for the position of "Nazi philosopher" denounced Heidegger's thought as "downright atheism" and "metaphysical nihilism."

Were such labels merely propaganda? Heidegger began as a seminarian studying for the priesthood and made strong pronouncements against irreligious "modernism" as having no universal commitments. Yet he soon distanced himself from the provincial Catholicism of his youth by leaving the seminary and taking up philosophy. Although he first worked in medieval scholasticism, by 1919 he wrote to his earlier Catholic mentor that he no longer found "the system of Catholicism" acceptable. He did not make the same judgment on "Christianity per se or metaphysics, the latter albeit in a new sense."

Yet that commitment seemed to fade. The aged Heidegger might have anointed himself with holy water whenever he chanced upon a church while hiking, but when he ominously said that "only a god can save us" in a 1966 Der Spiegel interview (published upon his death ten years later), he seemed to be talking about some "god" who is yet to be revealed, or perhaps the Greek gods to which the German poet Hölderlin had returned. In any case, the religion of his youth became in later life (as he put it) a thorn in his flesh: he could no longer accept it, but he couldn't quite leave it either. If "questioning is the piety of thinking," as Heidegger later claimed, then perhaps he adopted a new sort of piety.

Does Heidegger fare any better against the charge of "metaphysical nihilism"? Despite his breathtakingly brilliant phenomenological descriptions of human existence in Being and Time, what he calls Dasein or "being" really turns out to have nothing at its core. For Dasein's "being" is its ways of existing, not its commitment to any particular content. In place of a positive account of ethical values, Heidegger holds up the goals of authenticity, resolution and liberating care as ways to overcome the inauthentic "they" who partake in idle talk and allow their possibilities to be decided for them.

Even though Heidegger talks about such human phenomena as "fallenness" (which sounds remarkably like a Christian conception of sin), he repeatedly emphasizes that his account is scientific, not religious. The result is that Heidegger's "authenticity" turns out to be little more than another version of the modernistic ideal of individual autonomy, his "resolution" a resolve toward nothing in particular, and his "care" simply a concern for the self. When Jean-Paul Sartre formulated his own atheistic existentialism on the basis of these Heideggerian concepts, Catholic existentialist Gabriel Marcel criticized Sartre's philosophy as empty.

It is not too difficult, then, to see how Heidegger himself became a moth flying into the light of a Führer who promised to bring a new era into being and act as an "authentic" hero. Of course, Heidegger was also politically naïve, almost completely oblivious to the wider implications of his action, and emotionally detached to a dangerous degree. Hannah Arendt, with whom Heidegger began an affair when she was a student of 18, described him as someone who "lies always and at each opportunity." He was deceitful, disloyal, arrogant--and remorseful only when caught.

But Heidegger's allegiance to the National Socialists and his appointment to the rectorship of the University of Freiburg by Hitler cannot be explained simply by ignorance or deviance. Rather, Heidegger adopted Hitler--at least for a time--as his own personal Führer. In so doing, he was merely following his own earlier recommendation that authentic Dasein must "choose its hero."

Although his longtime friend Karl Jaspers was shocked that Heidegger took part in what Jaspers saw as a movement of mass hysteria, Heidegger himself never seems to have recognized his lapse of authenticity or acknowledged any wrongdoing. The best he could do in later days was to criticize his lack of judgment.

Much has been written on Heidegger's Nazi past, but Safranski gives us the most complete, accurate and fair account to date. Even so, the true degree of Heidegger's complicity is hard to determine. Though Heidegger makes quite a number of positive public references to Hitler and to Nazi ideas, Richard Rorty's statement (in reviewing Safranski's book) that the images of Hitler and Heidegger "blend into one another" is farfetched.

However much Heidegger turns out to be tainted by his Nazi connections, one must take his philosophy seriously. His impact--not only on philosophy and theology but on a wide variety of disciplines--has been so great that one cannot understand the current intellectual climate without at least some understanding of him. Jacques Derrida's claim that there is no thought in his work which is not dependent upon Heidegger is only a slight exaggeration. But another--and just as compelling--reason to read Heidegger is that he makes us think in fresh and helpful ways. This is what drew Arendt to him in the first place, and enabled her even later in life to speak glowingly of his mental acumen.

In one important sense, Heidegger does not give us a philosophy, for he provides us with nothing to believe in. But his focus on everyday human existence has helped philosophers realize how rooted their theoretical commitments are in practical life. Perhaps because Safranski is a freelance writer rather than a professional philosopher, he is able both to make Heidegger accessible and to do him justice.